linux-kernel - Re: [PATCH mm-unstable v3 4/5] mm: restart if multiple traversals raced

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Message-ID: <CAF6N3nVWPJT+qrcz2jGw+sNoKge1qgDGSYg5f0Ur8a6O8ziUQg@mail.gmail.com>
Date: Fri, 30 Aug 2024 10:45:00 -0700
From: Kinsey Ho <kinseyho@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	cgroups@...r.kernel.org, Yosry Ahmed <yosryahmed@...gle.com>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Hocko <mhocko@...nel.org>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, Tejun Heo <tj@...nel.org>, 
	Zefan Li <lizefan.x@...edance.com>, mkoutny@...e.com, baolin.wang@...ux.alibaba.com, 
	tjmercier@...gle.com
Subject: Re: [PATCH mm-unstable v3 4/5] mm: restart if multiple traversals raced

On Fri, Aug 30, 2024 at 3:04 AM Hugh Dickins <hughd@...gle.com> wrote:
>
> mm-unstable commit 954dd0848c61 needs the fix below to be merged in;
> but the commit after it (the 5/5) then renames "memcg" to "next",
> so that one has to be adjusted too.
>
> [PATCH] mm: restart if multiple traversals raced: fix
>
> mem_cgroup_iter() reset memcg to NULL before the goto restart, so that
> goto out_unlock does not then return an ungotten memcg, causing oopses
> on stale memcg in many places (often in memcg_rstat_updated()).
>
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> ---
>  mm/memcontrol.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6f66ac0ad4f0..dd82dd1e1f0a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1049,6 +1049,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
>                 if (cmpxchg(&iter->position, pos, memcg) != pos) {
>                         if (css && css != &root->css)
>                                 css_put(css);
> +                       memcg = NULL;
>                         goto restart;
>                 }
>
> --
> 2.35.3

Hi Andrew,

Would you prefer that I resend the series with Hugh's fix inserted?

Acked-by: Kinsey Ho <kinseyho@...gle.com>